1. Field of the Invention
The present invention relates to the creation of a desired light dispersion pattern using light transmitted via an optical waveguide from a remotely located source to a projection device. More particularly, the present invention relates to the use of a high intensity, high temperature light generator to provide light energy to a remotely located light head and, especially, to the coupling of light generated by such a source into one or more optical fibers for transmission to the light head. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Related Art
Attempts to illuminate an area using light generated by a remotely located light source and transmitted to a light head assembly or other luminaire via light guides are known in the art. To date, most light head assemblies designed for use with remote light sources have been mere variations on a single basic design. This basic design contemplates employment of a symmetric concave housing having an aperture within a central region thereof and a light transmissive lens which cooperates with the concave housing to define a chamber therebetween. An optical waveguide, i.e., a fiber or bundle of fibers, extends from the remote light source to the light head and thus transmits the light generated by the remote source to the light head housing. The optical waveguide, commonly referred to as a light pipe, projects through the aperture in the light head housing in a direction which is parallel to the axis of symmetry of the housing and terminates within the chamber of the housing. Since the intensity of the light emitted from the end of a light pipe decreases rapidly as the viewer moves off-axis, i.e., the light emitting end of a light pipe is effectively a very small diameter light source, the prior art has conventionally positioned a lens with a complex pattern of light refracting elements in registration with the discharge end of the light in an attempt to achieve a desired radiation pattern.
The use of a light pipe and remote light source in association with a head assembly offers a number of advantages over light head assemblies with integrated "point" light sources such as gaseous discharge tubes or high intensity incandescent lamps. Among these advantages are the absence of high temperatures and the elimination of the possibility of electric sparks within the light head assembly. The absence of high temperatures within the light head assembly precipitates the additional advantage of allowing the components of the light head to be fabricated from comparatively inexpensive low temperature plastic materials.
However, despite the significant potential benefits offered by light head assemblies designed for use with optical waveguides and remotely located light sources, such assemblies have not found widespread utility due to a number of inherent deficiencies. A major deficiency, as noted above, arises from the fact that a light pipe defines a very small area light source and the intensity of that source decreases rapidly off-axis. For example, in one commercially available optical fiber, approximately ninety percent (90%) of the available light may be measured within twenty-five degrees (25.degree.) of the axis of the light pipe. Thus, the area of a closely spaced surface which will be illuminated by light emitted from a light pipe is far too small to permit, for example, the light pipe to function as a spot or warning light. Accordingly, light head assemblies which employ a light pipe as the source of light must employ some means for dispersing the light transmitted by the light pipe.
Previous attempts to control the dispersion of light emanating from a light pipe have resulted in light head assemblies with serious limitations. A first limitation, as mentioned above, is imposed by the need to employ relatively complex lenses to refract the light emitted from the end of the light pipe. In addition to being expensive, the use of such a lens results in a comparatively high degree of attenuation of the available light. A second limitation of previously available light head assemblies which receive light via an associated light pipe resides in their elongated shape, i.e., their depth in the direction of travel of the light rays. Thus, in an effort to increase the area illuminated, previously available light head assemblies have spaced the emitting end of the light pipe a substantial distance from the refracting lens. While such spacing improves light dispersion, it also results in a volumetrically inefficient device. Light head assemblies employing such elongated housings are impractical for flush mounting on walls or for use where the space behind the supporting wall is severely limited such as, for example, in the case of a dome light in a vehicle. This problem is exacerbated because these prior art light head assemblies receive the light pipe from the rear of the assembly such that the axis thereof, and thus the axis of the emitted light beam, is oriented substantially parallel to the elongated dimension of the light head housing. Since the relatively fragile nature of optical fibers dictates that the light pipe be routed to prevent tight bends, substantial additional depth is required to mount these light head assemblies to a mounting structure. Thus, light head assemblies which employ a light pipe as the light source have found application in only a very limited number of environments.
Another major deficiency, which has previously precluded widespread use of high intensity light sources in combination with light heads, has its origin in the basic difficulty of coupling light into an optical fiber for transmission to the area to be illuminated. High intensity light sources, halogen lamps and HID lamps for example, produce considerable heat. Also, the light generated by such sources is not collumnated. Optical fibers, on the other hand, have a small diameter with a relatively small acceptance angle and are susceptible to thermal damage. Previous attempts to address these characteristics have resulted in highly inefficient coupling, i.e., a large percentage of the available light was not utilized, and/or the resulting systems have had a short service life as a consequence of thermal damage, and/or expensive lenses and/or reflectors and/or filters have been required. Examples of prior art light couplers may be seen from U.S. Pat. Nos. 3,455,622; 3,564,231; 4,233,493; 4,483,585; 4,883,333; 5,170,454; 5,271,077; 5,341,445; 5,428,509 and 5,491,765.